Process for the production of photographic positives



United States Patent Ofifice 3,236,641 Patented Feb. 22, 1966 3,236,641 PROCESS FOR THE PRODUCTION OF PHOTOGRAPHIC POSITIVES Daniel A. Nepela, Endwell, N.Y., assignor to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware N Drawing. Filed July 5, 1962, Ser. No. 207,764

8 Claims. (Cl. 9627) This invention relates to a novel process for the pro duction of photographic positives, said process possessing a simple processing procedure and a high intrinsic photographic speed.

The production of photographic positives has caused many problems to the skilled workers of the art. These problems were inherent in the procedures heretofore employed to obtain said photographic positives. Thus, if processes were employed to produce positives directly, slow photographic speed Was an inherent limitation. In order to overcome the disadvantage of slow speed, the art resorted to reversal processes. Although the reversal processes of the prior art did offer relatively high photographic speed, said reversal processes suffered from the disadvantage of requiring lengthy and cumbersome processing techniques which seriously impaired the overall efficiency and economy of these reversal processes.

Therefore, it is the object of this invention to provide a novel reversal process for the production of photographic positives, said process being characterized by the possession of high intrinsic speed and a simple processing procedure.

It has now been discovered that the above object can be obtained by the simple expedient of using for the exposure, a high speed electronic flash having a duration ranging from 10- to 10- seconds, and introducing a bleach step between exposure and the normal negative development procedure of conventional photographic films. The bleach treatment of the instant invention serves a twofold purpose in that it not only causes a complete removal of the negative latent image formed by the initial exposure, but also causes imagewise fogging of the image areas not so previously exposed.

The simplicity of the processing procedure of the instant invention can be very readily appreciated by reference to the following table wherein the processing procedure of the prior art for a conventional black and white photographic film is compared with the novel process of this invention:

TABLE 1 Prior Art Instant Process (1) Expose Expose (2) First developer Bleach (3) Shortstop Wash (4) Wash N on-fogging developer (5) Bleach Shortstop (6) Clearing solution Fix (7) Second exposure (8) Second development (9) Shortstop (10) Fix an alkali metal permanganate such as potassium permanganate and concentrated sulfuric acid in water. The amount of potassium permanganate employed can be from 0.1 to 2.0 grams per liter of water, although concentrations corresponding to about 0.5 grams per liter of water is preferred.

The amount of concentrated sulfuric acid employed can cover a wider range. Thus, 0.1 to 4 cubic centimeters of sulfuric acid can be employed per liter of water, although concentrations corresponding to about 0.25 cubic centimeter of sulfuric acid per liter of water is preferred.

The duration of the bleach treatment is not narrowly critical, although it has been established that l to 10 minutes is sufiicient in the ordinary case.

The light used for the exposure of the film is produced by an electronic flash of high intensity and a short dura tion of about 10 to 10- seconds.

Since the proposed direct reversal process has an extremely high low-intensity reciprocity failure, low while light level processing is possible, i.e., ASA-10 exposure for electronic flash, processing under a 25-watt tungsten ceiling light results in no image degradation. The flash intensity used must obviously be suflicient to create a negative latent image.

The gelatin silver halide emulsions employed are those which have been chemically sensitized during their preparation to form silver sulfide sensitivity centers. The emulsions employed contain silver bromide or silver bromoiodide grains of a fairly large size having a diameter of about 1 to 2 microns. These emulsions are either of the ammonia type or of the boil type. In the case of silver 'bromoiodide emulsions, the iodide concentration does not exceed 3 mole percent based on the weight of total halide. The amount of silver sulfide content of the emulsion corresponds from 1 to 8x10 molecules of silver sulfide per individual silver halide grain.

It is to be understood that this invention does not reside in non-fogging developer solutions whether black and white or color, shortstop solutions or fixing solutions. All the aforementioned categories are well known in the art for the processing of photographic materials as described, for instance, in US. Patent 2,629,660. This invention resides in combining an exposure of extremely short duration with a specific bleach step in an otherwise conventional process.

Another aspect of this invention involves the use of an alkali metal bichrornate, e.g., potassium dichromate bleach treatment of from 5 to 10 minutes prior to the potassium permanganate bleach. In this modification, the permanganate solution need not contain any sulfuric acid, but can be used in a pH range between 2.5 and 10.0. This technique allows for the obtainment of an extremely contrasty positive image since the dichromate bleach destroys the negative latent image first, so that the fogging ability of the permanganate bleach can be used to its fullest extent. Since the permanganate bleach has only a fogging function to perform, a higher contrast is obtained. In this aspect of the invention, the permanganate bleach time can be reduced to 1 to 2 minutes.

The dichromate bleach employed has the following composition:

Potassium dichromate "grams" 2-6 Concentrated sulfuric acid cubic centimeters 1-5 Water to make liters 1 The novel process of this invention can be employed in both black and white and color development. It can be used with emulsion systems containing lipophilic or hydrophilic color former dispersions. In this instance, a developer is employed which contains an aromatic amino developing agent, the oxidation products of which are capable of coupling with the color formers present to form azamethine, indophenol or phenazine images. Such processes are described in US. Patents 2,179,228, 2,179,239, 2,186,849, 2,220,187, 2,486,440, 2,524,741 and 2,701,766.

It is also practicable Using color procedures wherein .both the color former and the color developer are contained in the developing solution, as described in US. Patents 1,897,866, 1,900,870, 1,928,709 and 1,980,941.

The following examples will illustrate the novel process of the invention.

Example I A conventional gelatin silver halide photographic film was exposed under a pattern with a high intensity electronic flash for 10 seconds. The film was then treated with the following bleach solution for to minutes:

Potassium permanganate grams 0.5 Concentrated sulfuric acid cubic centimeters 0.25 Water to make liters 2 The film was then washed and treated with the following non-fogging developer:

Metol grams 1.0 Ascorbic acid do 3.0 Borax .1OH O do 20.0 Water to make liter 1 After normal shortstop and normal fixation, a photographic positive was obtained of good quality.

Example II The process of Example I was repeated with the exception that after exposure, the film was treated with the following bleach:

Potassium dichromate grams 4 Concentrated sulfuric acid cubic centimeters 2.5 Water to make liters 1 After washing, the film was processed exactly as in Example I except that the potassium permanganate bleach time was reduced to 1 to 2 minutes and the sulfuric acid was omitted from the solution. The developer solution used had the following composition:

Water cubic centimeters 850 Ethylenediamine tetraacetic acid grams 1.5 Potassium hydroxide do 22 Sodium sulfite do p-Methylaminophenol sulfate do 5 Hydroquinone do 50 Potassium carbonate do 90 Sodium bromide do 15 Benzotriazole do 0.8 Water to make liters 4 A good photographic positive was obtained which possessed a higher contrast than that obtained in Example I.

What is claimed is:

1. In the process for developing an imagewise exposed light sensitive silver halide emulsion wherein said exposed emulsion is first treated with a non-fogging developer, followed by shortstopping and fixing, the improvement which comprises using as the exposure light source an electronic flash having a duration ranging from l0- to 10 seconds, the intensity of the exposure being sufficient to create a negative latent image, and subjecting said imagewise exposed emulsion to an aqueous bleach solution containing an alkali metal permanganate and sulfuric acid prior to treatment with said non-fogging developer so as to produce a photographic positive.

2. The process of claim 1 wherein said bleach solution contains from 0.1 to 2.0 grams of potassium permanganate and from 0.1 to 4 cubic centimeters of concentrated sulfuric acid in 1 liter of water.

3. The process of claim 1 wherein said bleach consists of 0.5 gram of potassium permanganate and 0.25 cubic centimeter of concentrated sulfuric acid in 1 liter of water.

4. The process of claim 3 wherein said bleaching treatment is carried out from 1 to 10 minutes.

5. In the process for developing an imagewise exposed light sensitive silver halide emulsion wherein said emulsion is first treated with a non-fogging black and White developer, followed by shortstopping, fixing and washing, the improvement which comprises exposing said emulsion imagewise with the light of an electronic flash having a duration ranging from 10* to 10" seconds, the intensity of the exposure being sutficient to create a latent negative image, and subjecting said imagewise exposed emulsion to an alkali metal dichromate bleach followed by an alkali metal permanganate bleach having a pH ranging from 2.5 to 10.0 prior to treatment with said non-fogging developer so as to produce a photographic positive.

6. The process of claim 5 wherein said potassium permanganate bleach consists of from 0.1 to 2.0 grams of potassium permanganate and 0.1 to 4 cubic centimeters of concentrated sulfuric acid in 1 liter of water.

7. The process of claim 6 wherein said potassium dichromate bleach consists of 2 to 6 grams of potassium dichromate, 1 to 5 cubic centimeters of concentrated sulfuric acid and sufficient water to make 1 liter of solution.

8. A process for the production of photographic positives which comprises treating a light sensitive silver halide emulsion in the following manner in exact order:

(a) exposing said emulsion through a pattern with light of high intensity and a duration ranging from 10' to 10 seconds, the intensity of the light being sufficient to create a negative latent image,

(b) bleaching said imagewise exposed emulsion for l to 10 minutes with a bleach consisting of 4 grams of potassium dichromate, 2.5 cubic centimeters of concentrated sulfuric acid and suflicient water to make 1 liter of solution,

(c) washing said emulsion with water (d) bleaching for 1 to 2 minutes with a bleach consisting of 0.5 gram of potassium permanganate, 0.25 cubic centimeter of concentrated sulfuric acid in 1 liter of water,

(e) washing,

(f) developing with a non-fogging developer,

(g) shortstopping,

(h) fixing,

(i) and washing.

References Cited by the Examiner UNITED STATES PATENTS 2,810,648 10/1957 Hineline 9660 OTHER REFERENCES Hunt, Proceedings of the Fifth International Congress on High-Speed Photograph, pages 76 to 79, 1962.

NORMAN G. TORCHIN, Primary Examiner. 

1. IN THE PROCESS FOR DEVELOPING AN IMAGEWISE EXPOSED LIGHT SENSITIVE SILVER HALIDE EMULSION WHEREIN SAID EXPOSED EMULSION IS FIRST TREATED WITH A NON-FOGGING DEVELOPER, FOLLOWED BY SHORTSTOPPING AND FIXING, THE IMPROVEMENT WHICH COMPRISES USING AS THE EXPOSURE LIGHT SOURCE AN ELECTRONIC FLASH HAVING A DURATION RANGING FROM 10**-3 TO 10**-4 SECONDS, THE INTENSITY OF THE EXPOSURE BEING SUFFICIENT TO CREATE A NEGATIVE LATENT IMAGE, AND SUBJECTING SAID IMAGEWISE EXPOSED EMULSION TO AN AQUEOUS BLEACH SOLUTION CONTAINING AN ALKALI METAL PERMANGANATE AND SULFURIC ACID PRIOR TO TREATMENT WITH SAID NON-FOGGING DEVELOPER SO AS TO PRODUCE A PHOTOGRAPHIC POSITIVE. 